Retroreflective materials are employed for various safety and decorative purposes. Particularly, these materials are useful at nighttime when visibility is important under low light conditions. With perfect retroreflective materials, light rays are reflected essentially towards a light source in a substantially parallel path along an axis of retroreflectivity. Retroreflective materials can be used as reflective tapes and patches for clothing, such as vests and belts. Also, retroreflective materials can be used on posts, barrels, traffic cone collars, highway signs, vehicles, warning reflectors, etc. Retroreflective material can include arrays of randomly oriented micron diameter spheres or close packed cube-corner (prismatic) arrays.
Cube-corner or prismatic retroreflectors are described, for example, in U.S. Pat. No. 3,712,706, issued to Stamm on Jan. 23, 1973, the teachings of which are incorporated by reference herein. Generally, the prisms can be made by forming a master negative die on a flat surface of a metal plate or other suitable material. To form grooves 60 degrees apart are inscribed in the flat plate. The die is then used to process the desired cube-corner array into a rigid flat plastic surface.
Further details concerning the structures and operation of cube-corner microprisms can be found in U.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15, 1972, the teachings of which are incorporated by reference herein. A method for making retroreflective sheeting is also disclosed in U.S. Pat. No. 3,689,346 issued to Rowland on Sep. 5, 1972, the teachings of which are incorporated by reference herein. For example, cube-corner microprisms can be formed in a cooperatively configured mold. The prisms can be bonded to sheeting, which is applied thereover to provide a composite structure in which the cube-corner elements project from one surface of the sheeting.
Retroreflective materials can be particularly useful when visibility is critical such as under emergency conditions. For example, retroreflective materials can be used for firefighters' coats and protective clothing. However, the conditions that firefighters are exposed to can be harsh, especially in regard to excessive heat and temperature conditions. Many retroreflective materials are made of plastics that soften at temperatures of about 100° C. The softened plastic in such materials can begin to flow causing the material to lose its retroreflectivity and thereby impair visibility. The National Fire Protection Association (NFPA) has established standards that can be used to evaluate clothing and retroreflective structures intended to be worn by firefighters.